Conventionally, some plastic lenses for eyeglasses are produced by injection molding using a thermoplastic resin such as a polycarbonate resin or a methacrylic resin. Even in the case of a plastic lens having a complicated optical surface shape such as a progressive addition lens, highly accurate molding is possible by transferring the cavity shape of a mold.
For example, Patent Document 1 discloses a method for molding a plastic lens with a high degree of accuracy by controlling the temperature of a mold by heating through insertion of a high-frequency heating means into a mold in an opened state during clamping.
Further, as a method for enhancing transferability when the shape of a cavity is transferred in an injection molding method, Patent Document 2 discloses a method in which a mold is vibrated by ultrasonic waves when injecting and filling a molten resin in a cavity. Patent Document 3 discloses a method in which carbon dioxide is injected into a gap between the resin filled in the cavity and the cavity surface.
Further, as a method for molding a plastic lens for eyeglasses, a method called an injection compression molding method is known. For example, in Patent Document 4, one example of such an injection compression molding method is disclosed. According to the injection compression molding method, by further compressing a resin that has been filled by injection in the cavity of a mold, shrinkage of the molten resin is compensated, whereby uniform and higher degree of accuracy in shape can be obtained, thus leading to more accurate molding.
In the injection mold used in the injection compression molding method of the cited document 4, insert molds as a mold for forming an optical lens for molding an optical surface of a lens, that is exchangeable according to the kind of a lens, are accommodated within the inside of an insert guiding member respectively provided in a movable mold and a fixed mold, whereby a cavity for forming a lens can be formed.
The insert mold as a mold for forming an optical lens is normally made of steel such as maraging steel, beryllium-copper alloy or the like. However, for capability of molding smoother and more accurate optical surface or for other reasons, when a plastic lens is molded, use of a glass-made mold may be advantageous. Therefore, a mold for forming an optical lens obtained by connecting a glass substrate in which a molding surface for molding an optical surface of a lens is formed with a metal pedestal is known (see Patent Document 5).